In gas turbine engines parts deal with high material temperatures making it usually necessary to provide cooling to these parts. Due to uneven heating, cooling needs to be adjusted.
Typically, a worst case map of hot-spots is established from calculations and with highly expensive experimental testing. The cooling system is designed to cope with this hot-spot map. Where the position of the hot-spot(s) is known and doesn't move significantly during operation, similar parts with varying cooling passages can be applied at the expense of standardization with effects on lead times and spares stocks.
However, the heating patterns cannot be established over all combinations of the variation of parameters, like inlet temperature and pressure, fuel type, quality and composition, or machine load, which will be experienced in service. Manufacturing variation can also lead to variation between nominally identical parts. Furthermore, service replacement and equipment wear can also change the heating patterns during the operating life of the equipment.
Therefore, robust design usually involves the use of more cooling air than is strictly necessary with impact on engine efficiency and thermal stresses between joined hotter and cooler areas of the cooled part which reduces life of the engine.
Other, dynamic approaches adjust cooling during operation relying on (failure-prone) sensors and valves with contact surfaces between parts in relative motion (subject to wear).
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